The reference in this specification to any prior publication, or information derived from it, or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that the prior publication, or information derived from it, or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
Many products, in particular household and portable devices are designed to be powered by batteries, such as AA-cell, C-cell and D-cell batteries. Disadvantages when using such traditional batteries include: relatively short operational lifetime and limited shelf-life i.e. expiry due to degradation of the internal (closed system) components over time even when not in use. These devices are therefore also alternatively powered by other sources, including solar power or kerosene.
Disadvantages of using kerosene as an alternative power source include: high monthly costs; environmental pollutant (millions of tonnes of CO2 and black carbon released into the atmosphere contributing to global warming); adverse impact on health (e.g. lungs, eyes, skin and general wellbeing); potential fire hazard (due to flammability); safe storage and regular purchase issues; not suitable as a power source for some products and devices (such as emergency beacons, radios, communications equipment and recharging docks for USB devices); and even the potential for poisoning caused by accidental drinking due to confusion as a beverage.
Disadvantages of using solar energy as an alternative power source include: variability in amount and duration of sunshine (particularly during winter); impact of rain (which can reduce solar potential to near zero during tropical rainy/monsoonal season); cloudy conditions and fog can reduce power generation (by approximately 10-80%); shadows and haze can also reduce the effectiveness of solar power; impact of the sun's latitude (angle of the sun) and need to adjust position of solar capture device for effective capture; must be located outdoors to capture sunshine leaving them at risk of damage from external elements as well as theft; and limitations of solar devices themselves in that they are not rechargeable so must be disposed of at the end of their life.
Metal-air fuel cells, such as magnesium-air fuel cells can also be used as an alternative to traditional batteries. Metal-air fuel cells are considered to offer certain advantages including: high energy density; low price; and long storage potential.
Generally speaking, metal-air fuel cells operate by suspension in an ionic aqueous solution, such as sea water or other saline solutions, which acts as the electrolyte between the air cathode and anode. The air cathode is exposed to oxygen to allow the electrochemical reaction to occur. By-products of this electrochemical reaction include:    a) release of hydrogen gas (and minute amounts of chlorine gas); and    b) waste materials from anode degradation (e.g. metal hydroxides).
Metal-air fuel cell technology is not without its disadvantages, including: leakage of the electrolyte from the cell; exposure of the electrodes to excess electrolyte causing performance interference; sealing problems; gas (e.g. hydrogen and chlorine) build-up and venting issues; dangerous temperature and pressure build up caused by runaway exothermic redox reactions, waste management issues associated with anode degradation (e.g. impaired cathode life caused waste material accumulation within the fuel cell in the absence of regular cleaning and electrolyte replacement).
Magnesium-air fuel cells have a typical lifespan of 50 to 100 hours before requiring replacement of the anode. Performance of the air cathode also often diminishes very rapidly after only 100 to 200 hours of use, or even during storage after initial use. Some metal-air fuel cells require stringent regular maintenance and cleaning activities by the user in order to maximize air cathode life.
Typical metal-air fuel cell configurations are exemplified by: U.S. Pat. No. 3,519,486 (7 Jul. 1970), Huebscher, R. G. et. al.; and U.S. Pat. No. 3,963,519 (15 Jun. 1976), Louie, H. P.
U.S. Pat. No. 3,519,486 describes a trapped electrolyte fuel cell that includes internal reservoir(s)/chamber(s) in the bottom of the cell to capture excess electrolyte. The captured excess electrolyte forms electrolyte pool(s) in which the electrodes and a matrix are positioned. The matrix is made of a material resistant to potassium hydroxide, such as a fibrous asbestos matting (column 2, lines 4-5). The cell must be sealed to prevent leakage of the electrolyte. Further, as the reservoir(s) are positioned in the bottom of the cell, the cell must be positioned in an upright orientation to ensure electrolyte pooling and operation of the cell.
U.S. Pat. No. 3,963,519 describes another trapped electrolyte fuel cell with a protective shield spacer. The spacer provides structural strength to the cell and protects the cathode while permitting air to pass over the entire surface of the cathode. This design was considered an advance over earlier heavy-framed metal/air battery constructions that were considered unsuitable for use as primary and secondary lightweight metal-air cells of AA, C and D cell configurations. A liquid-tight configuration to internally seal the electrolyte is described.
Neither U.S. Pat. No. 3,519,486 nor U.S. Pat. No. 3,963,519 describes a process for removing or isolating accumulated anode-degradation waste and/or venting by-products to alleviate pressure build-up.
Development of metal-air fuel cell technologies is ongoing. For example Aqua Power System, Japan is presently seeking to advance metal-air fuel cell technology as described in at least the following three PCT patent applications and marketed as their “Realistic Magnesium Air Fuel” (RMAF) system technology    (http://aquapowersystems.com/technology/how-aqua-powers-technology-works/, website accessed 19 Dec. 2016).
WO2014/097909 (Aqua Power System, Japan; also published as US2015/0340704 A1), discloses a metal-air fuel cell with a layered cathode body including water repellent and electrically conductive carbon material(s). The resulting fuel cell is described as highly water repellent, air permeable, and leakage resistant.
WO02014/115880 (Aqua Power System, Japan; also published as US2015/0364800 A1), provides a magnesium-air fuel cell with a comparatively shorter distance between the anode and the cathode to improve the electrochemical reaction. The height and width of the fuel cell, relative positioning of the anode and cathode, and use of a water supply pipe further including a reaction gas discharge pipe is said to generate a stable supply of power for a relatively long period of time. However, as the inlet to the reaction gas discharge pipe may be located within the cell, the reaction gas discharge pipe may undesirably leak electrolyte and/or gas.
WO2014/115879 (Aqua Power System, Japan; also published as US2015/0380693 A1), discloses a magnesium-air fuel cell that can be turned on and off by virtue of a lid, that when fastened brings the terminals into contact to switch the power ‘on’ and when loosened, turns the power ‘off.’
RMAF technology is understood to be incorporated into a number of commercial products including a water-activated 1.5V AA battery    (http://aquapowersystems.com/products/batteries/, website accessed 19 Dec. 2016) However, as disclosed in the website, the Aqua Power battery is configured as a fixed-sized, closed system which requires manual introduction of the electrolyte via a small, hand-operated pipette.
Fluidic, Inc., (US) is another company presently seeking to advance metal-air fuel cell technology. The Fluidic, Inc., platform technology is understood to be incorporated into the first commercialised rechargeable zinc-air battery (http://fluidicenergy.com/technology/, website accessed 19 Dec. 2016).
Fluidic, Inc., describe various advances in metal-air fuel cell technology including, for example: use of a dopant to increase the conductivity of the metal fuel oxidation product, i.e. the anode is doped degenerately (WO2014/062385, Fluidic, Inc.); use of additives in the ionically conductive medium to enhance electrodeposition and/or extending the cell's capacity (WO2014/160144, Fluidic, Inc.); hetero-ionic aromatic additives (WO2014/160087, Fluidic, Inc.); additives comprising poly(ethylene glycol) tetrahydrofurfuryl; and control of the concentration of additives in the ionic conductive medium (WO2016/123113 and WO2012/030723, Fluidic, Inc.). Other claimed advances resulting from design modifications include: to accommodate a gaseous oxidant receiving space (WO2013/066828, Fluidic. Inc.); a catch tray containing a catalyst material to catalyse the oxidation of waste particulates (WO2012/012364, Fluidic, Inc.); an anode having a scaffolding structure (WO2011/163553, Fluidic, Inc.); a fuel cell having a plurality of electrodes (WO2011/130178 and WO2012/037026, Fluidic, Inc. respectively) and multiple fuel cell systems (WO2011/035176, WO2012/106369 and WO2010/065890, Fluidic, Inc. respectively).
In general, the Fluidic, Inc. metal-air fuel cell technology is akin to conventional rechargeable batteries in that the process is reversible because the anode is not consumed and further that the anode is “doped” or coated to stop it from degrading.
Despite numerous advances in metal-air fuel cell technology, there remains an ongoing need to overcome certain disadvantages associated with the technology and to provide new sources of direct current power particularly in the form of batteries, for use in devices and products which are affordable, accessible, environmentally friendly (re-usable, recyclable), have a long-life (shelf and/or operation), are reliable and safe.